Chap. II. LIMITS OF THE CLASS. 105 



spermatic particles in the s^^erm cells has been observed ; their special homologies 

 Avith the highest Discophoraj have been made out ; and nothing is wanting to prove 

 that the naked-eyed Medusre, in their adult condition, are genuine Acalephs, closely 

 allied to the covered-eyed Discophora\ The naturalists who, having identified them 

 with the so-called sexual Ijunches of the Siphonophoi'o?, would consider them as 

 free sexual organs because these bunches appear to them to be sexual organs, 

 and not clusters of sterile Meduste, are bound to show that spermaries and ovaries 

 may have the structure of perfect Meduste, that is, a gelatinous bell, radiating and 

 circular chymiferous tubes, and a proboscis ; not simply by affirming that certain low 

 sessile Meduste are sexual oi'gans, but by adducing the evidence of a similar structure 

 of the sexual organs in other Acalephs. The burden of furnishing that proof rests 

 with them, because other naturalists have already shown that these supposed free 

 sexual organs, including the gonocalyx of the Diphyidas and the androphores and 

 gyuophores of the Physophoridai, not only exhibit all the characteristic structural 

 features of genuine Acalejjhs, but are themselves either male or female individuals 

 provided with ovaries and spermaries. 



As the divergence of opinions upon this point has arisen from the peculiar 

 phenomena known as alternate generations, it is proper that we should now turn 

 our attention to this subject for a moment, and examine critically the dis- 

 tinctive features of the various facts now generally considered as constituting one 

 peculiar mode of reproduction ; since, from the beginning, heterogeneous phenomena 

 have l>eeu confounded under that name. Without stepping beyond the limits of 

 the class of Acalephs, we have, in the first place, the case of the higher Discophorae, 

 in which, as for instance in Aurelia and Cyanea, the young Ijorn from eggs (PI. 

 X. Fif/s. 1 and 2, and PI. X\ Figs. 16-24) as independent, locomotive, single indi- 

 viduals (PL X. Ficjs. 3 to 10, and PI. X^ Fir/s. 25 to 3G), become attached (PI. X. 

 FIffs. 11, 12, 13, and ll), and then tentacles appear gradually (PI. X. Fic/s. 13 and 

 14), the young thus assuming the form of Hydrte, with an increasing number of 

 tentacles (PI. X. Figs. IG to 37, and PI. X''. Figs. 11 to 15). The body is next 

 furrowed. by transverse grooves, and assumes an annulate appearance, and the rings 

 thus formed (PI. XI. Fig. 19) become gradually more distinct and more numerous, 

 until the Hydra is changed into a Strobila, which is only a Hydra undergoing a 

 process of transverse segmentation. As the process of isolation resulting from a 

 deeper and deeper contraction of the ambulacral segments l^ecomes more complete, 

 the whole resembles a pile of scalloped saucers, with a fringe of tentacles; next, the 

 uppermost segment drops ofl'; then the next disk, then the next, and so on until 

 in the end, each disk has separated successively from that below (PI. XL Fig. 29), 

 and the base of the original Hydra, having reproduced tentacles, remains alone, 

 perhaps Avith a fcAv disks attached to it (PI. XL Figs. 1, 4, and 17), or Avith a 



A'OL. HI. 14 



